This invention relates to a method of working single-crystal or polycrystalline diamond used in a tool, a heat sink or the like, and provides a working method in which diamond cutting and surface smoothing of diamond can be performed with high efficiency and high precision.
Diamond has the highest hardness among all the substances, so that diamond is extremely difficult to be worked. In the case of single-crystal diamond, data regarding the surface orientation and direction in which the working can be relatively easily conducted are known to some degree. Though in the limited range, in accordance with the data, the grind working is conventionally conducted by scaife abrasion. However, in the case of polycrystalline diamond, the diamond particle constituents are orientated in any directions. In this case, the scaife abrasion or the like may be conducted, but it is difficult to smooth the surface.
On the other hand, regarding the cutting, a discharge machining can be applied to a sintered body which is sintered by using a conductive sintering assistant. However, this method cannot be applied to diamond having no electric conductivity, such as single-crystal diamond, sintered diamond which is sintered by using a nonconductive sintering assistant, and vapor-phase synthetic diamond. Conventionally, therefore, the cutting work is thermally performed using laser such as CO.sub.2 laser, CO laser, and YAG laser. However, since diamond is transparent to such laser light, this method has a disadvantage in that the utilization efficiency of optical energy is poor, that is, the working efficiency is poor.
The working is performed by irradiating diamond with infrared light having a wavelength of 1 .mu.m or more to heat diamond, so as to fuse, graphitize and oxidize the diamond, and hence portions in the peripheral of the area to be worked are thermally affected to be degraded. Moreover, since the cutting margin should be set large, there arises a serious problem in that the working precision is degraded.
When the cutting work is performed with laser in a conventional manner, peripheral portions of diamond are degraded by heat. Therefore, the degraded peripheral portions are required to be mechanically removed by scaife abrasion or another method. In the case where laser is used for smoothing the surface, the laser is transmitted to reach the inside and base members which must not be worked, thereby causing an adverse influence to be exerted, in addition to the deterioration of the peripheral portions of diamond by heat. In order to avoid these adverse influences, it is required to provide a countermeasure by which the incident angle of laser is restricted so that only the surface is illuminated, or which suppresses the scattering of laser at the surface.
In the case of performing the grinding work by scaife abrasion or another method, the abrasion is conducted by heat. Therefore, diamond is heated to several hundreds of degrees Celsius by frictional heat, resulting in that the diamond body is inevitably adversely affected. It is known that diamond in the air starts at about 600.degree. C. to be graphitized and oxidized, to deteriorate. In the case of scaife abrasion, moreover, it is difficult to fix a work piece. If the work piece is too small or has an indefinite form, the abrasion for such a work piece is extremely difficult to conduct, and thus the operability is poor. Sometimes, there occurs a case where the work cannot be performed. Moreover, the work by scaife abrasion has a problem in that it necessitates much time.